Surface ablation of biological tissue is a process used in a variety of medical procedures. An ablation process may be used to remove unwanted tissue and can also be used, in certain tissues, to stimulate or induce regeneration and renewal.
Various cosmetic treatments are known and widely used that attempt to reduce the effects of ageing through surface ablation or other minor trauma of the skin to induce regeneration thereof. The skin is made up of two main layers, the dermis and the epidermis which provides the exposed surface. The epidermis comprises layers of maturing skin cells one on top of the other, with the outermost layer being a layer of dead cells that is shed and replaced by layers underneath as they reproduce. These cosmetic procedures aim to improve the appearance of patient's skin with the intention of, for example, reducing visible fine lines and wrinkles, ‘rejuvenating’ the skin to remove pigment spots and providing a smoother finish, and improving the appearance of scar tissue, such as scars resulting from acne.
These cosmetic procedures typically fall into three categories: mechanical procedures, chemical procedures and laser procedures.
‘Mechanical’ procedures achieve the resurfacing of the skin by removing unwanted skin by mechanical abrasion. Microdermabrasion is a light, non-invasive non-surgical cosmetic procedure that works to achieve the removal of dead skin cells in the topmost layer of the epidermis by action small abrasive granular crystals of, for example, aluminium oxide. Microdermabrasion is useful for cosmetically treating fine irregularities in the texture of the skin, fine wrinkles and superficial scarring, but it is temporary in its effect and it is typically not capable of improving the appearance of the skin by deep resurfacing and rejuvenation to remove more significant wrinkles and scarring.
Dermabrasion, on the other hand, is a more significant, surgical procedure for effectively removing the top to mid-layers of the skin (the epidermis and even the dermis) using abrasive wheels, brushes and sandpaper to mechanically attack and remove unwanted skin. As deep layers of skin tissue are removed, significant bleeding can often result and so a local or even general anesthetic is required and dermabrasion is typically performed by a medical professional in a medical or surgical setting. The deep ablation and resurfacing of skin by dermabrasion can, following recovery, achieve an improved skin appearance by removing deeper scarring, fine wrinkles and skin irregularities. However, with dermabrasion there is no fine depth control, and the abrasives have to be applied to a wide area of the skin in order to ‘blend’ the finish, preventing effective treatment of localized irregularities. The traumatic effect on the skin and required recovery time of dermabrasion is significant.
Chemical peel procedures use a variety of chemical types which when applied directly to the skin, change the skin composition and cause unwanted skin to slough off the surface. Lighter peels can be applied in non-medical settings in cosmetic skincare treatment centres and these can achieve moderate, longer term improvement in the appearance of fine wrinkles and minor skin irregularities. However, medium and higher strength peels that remove skin to deeper layers are surgical treatments that require the expertise of medical practitioners to understand the effect of the chemical peel mixture, but can achieve improved skin appearance of more significant wrinkles and irregularities. However, there is no fine depth control available in any chemical peels, and the peel treatment must be applied to the whole area of the skin—e.g. the face, preventing localized treatment. Chemical peels can often require long recovery periods and also side effects on the skin such as photosensitivity. Repeat peels may also be needed to achieve a desired effect for a longer term.
Laser skin resurfacing, however, has addressed a number of shortcomings of dermabrasion and chemical peels and is capable of achieving skin resurfacing and rejuvenation to significantly improve skin appearance, and can even reduce the appearance of deeper wrinkles including frown lines and crows feet. Here, a CO2 or Er:YAG laser light is used to act to rejuvenate the skin by dissociating the molecular bonds in the surface and subsurface layers of the skin to induce trauma and cause the skin (in particular the layers of the epidermis) to rejuvenate. In addition, the deep heating of the lower layers of the skin by the laser is understood to stimulate fibroblasts in the dermis to form new collagen and elastin to increase the turgor (elasticity) and thickness of the skin, helping to reduce the appearance of deep wrinkles and aging skin. Rather than laser treating the entire surface of the skin, laser treatments typically are delivered to a fraction of the skin in a pattern of pinpoints (or Microscopic Treatment Zones, MTZ) spread over an area of the skin, between which healthy skin remains, which reduces healing time and recovery. Compared to dermabrasion and chemical peels, laser treatment does allow a degree of localized control based on the requirements of the skin area by area. However, this pinpoint patterning of the ablated skin can leave a visible patterned finish even after recovery that is emphasized should further treatment (such as a facelift) be undertaken. As a result of this finish, laser skin resurfacing is not suitable for using in treating small ‘zones’ of skin, as the pattern of pin pricks cannot be blended.
A metric useful for assessing energy sources for ablation is fluence, defined for pulsed laser ablation energy sources as the energy of the laser pulse (Joules, J) divided by the area of the incident laser spot (in cm2). Generally, the greater the fluence of the laser, the greater the depth of penetration and rejuvenation of the dermis. For a typical comparison, energy levels achieved using one, well-known system marketed under the trade name Fraxel™ re:pair™ available from Fraxel range from 5-70 mJ/MTZ, giving a high level of equivalent fluence in the order of a hundred Joules per cm2. Thus a high, concentrated energy transfer is achievable with pulsed fractionated laser systems to a low level of the dermis. For the Fraxel™ re:pair™ system, the penetration depth achievable is from 200-1500 microns. As such, laser treatment is capable of achieving improved deep wrinkle reduction and skin resurfacing with significantly reduced bleeding, side effects and recovery time compared to dermabrasion and strong chemical peels. As a result, laser skin resurfacing can be provided as a cosmetic non-surgical treatment in a non-medicalised setting, administered by a trained operator who is not necessarily a medical professional.
It has been suggested that plasma, the fourth state of matter, formed by, for example, ionizing a gas, could be used to rejuvenate skin. One such system using a gas plasma for ablative tissue rejuvenation was developed by Rhytec Ltd in the United Kingdom and is now marketed under the brand name of NeoGen™ by Energist Ltd. of United Kingdom, for which more information is currently available from the following URL: http://www.energistgroup.com/.
Rhytec Ltd's International patent application publication no. WO 2001/62169 A2 discloses the technology underlying the development of the NeoGen™ system. The Rhytec Ltd published patent application discloses a handheld surgical instrument having a conduit carrying nitrogen gas and an electrode structure and radio frequency pulsed power source arranged to produce a dielectric barrier discharge inside the conduit that weakly ionizes the nitrogen gas to produce a low energy, non-thermal plasma to be emitted at a nozzle of the conduit. The plasma produced at the nozzle is used in the cosmetic treatment of fine wrinkles and skin irregularities and operates to rapidly transfer heat to the dermis to stimulate collagen production and increase skin elasticity and thickness. However, unlike with laser treatments, this dermal heating and rejuvenation does not occur at the same time as direct ablation (e.g. by vapourisation) of the upper layers of the epidermis. Thus the side effects and down time of this treatment are less significant than for laser treatment. However, the energy levels transferrable by the NeoGen™ system are only 2-6 Joules per pulse across the size of the plasma plume, are relatively low and unconcentrated compared to laser skin resurfacing, being spread over a spot size of over a square centimetre, giving a low equivalent fluence value on the order of 1 J/cm2. While, unlike for laser light, absorption of the plasma energy is not dependent on the presence of a particular cholorophore (e.g. water present in cells for CO2 lasers) leading to more uniform absorption across cell types, skin types and structures, the low equivalent fluence of the NeoGen™ plasma system means that its ability to reliably and effectively treat deep wrinkles and achieve significant skin resurfacing is questionable. The lack of any direct skin ablation, combined with the low fluence, means that the usefulness of the NeoGen™ system for skin resurfacing and removal of significant skin irregularities and wrinkles is very limited. Indeed a large number of repeat procedures may be needed to achieve any noticeable benefit for anything more significant than fine wrinkles and minor skin imperfections.
Non-ablative treatments to improve the appearance of ageing skin include the use of dermal fillers, botox and collagen which are injected into the skin. However, these are invasive interventions that have significant side effects on the appearance of the individual by bulking out skin and paralyzing muscles. These treatments do not themselves fundamentally rejuvenate the skin, but rather they seek to achieve improved appearance by ‘sculpting’ the skin and ‘filling out’ wrinkles, which can appear unnatural.
Another non-ablative treatment is radio frequency, infrared or ultrasound skin tightening therapy in which radio frequency, infrared light or ultrasound waves are used to heat the skin to attempt to promote collagen formation to tighten the skin. However, the effect of these treatments is not significant and is only short term in benefit, requiring a large number of repeat sessions.
In view of the above, there is an interest in new treatments for promoting skin rejuvenation and reducing the appearance of wrinkles and skin irregularities. In addition, the ablation and trauma principle is also used for other surgical purposes, notably wound debridement and tissue regeneration.
It is in this context that the present invention is devised.